Anatomy Notes Day 24 - Lisa Nelson PDF

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Lisa Nelson...

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The Autonomic Nervous System ● ● ● ●

Consists of motor neurons that Innervate smooth muscles, cardiac muscle, and glands Make adjustments to ensure optimal support for body activity Shunts blood to areas that need it and adjusts heart rate, blood pressure, digestive processes ● Operate via subconscious control ● Also called involuntary nervous system or general visceral motor system ● Both somatic and autonomic nervous systems have motor fibers but differ in ○ Effectors ○ Efferent pathways and ganglia ○ Target organ responses to neurotransmitters Effectors ● Somatic nervous system innervates skeletal muscles ● ANS innervates cardiac muscle, smooth muscle, and glands Efferent pathways and ganglia ● SNS: cell body is in CNS, and a single, thick, myelinated group ● A axon extend in spinal or cranial nerves directly to skeletal muscle ● ANS: pathway uses a two-neuron chain ● Preganglionic neuron: cell body in CNS with thin, lightly myelinated preganglionic axon extending to ganglion ● Postganglionic: outside CNS, cell body synapses with preganglionic axon in autonomic ganglion with nonmyelinated postganglionic axon that extends to effector organ Neurotransmitter Effects ● Somatic Nervous System ○ All somatic motor neurons release acetylcholine (ACh) ○ Effect is always stimulatory ● ANS ○ Preganglionic fibers release ACh ○ Postganglionic fibers release norepinephrine or ACh at effectors ○ Effect is either stimulatory or inhibitory, depending on type of receptors Overlap of Somatic and Autonomic Function ● Higher brain centers regulate and coordinate both systems ● Most spinal and many cranial nerves contain both somatic and autonomic fibers ● Adaptations usually involve both skeletal muscles and visceral organs ● Ex. Active muscles require more oxygen and glucose, so ANS nerves speed up heart rate and open airways Divisions of Autonomic Nervous System ● Two arms of ANS ● Parasympathetic division: promotes maintenance functions, conserves energy ● Sympathetic division: mobilizes body during activity ● Dual innervation: all visceral organs are served by both divisions, but these divisions cause opposite effects ● Dual innervation between two divisions maintains homeostasis

Role of the parasympathetic division ● Keeps body energy use as low as possible, even while carrying out maintenance activities ● Directs digestion, diuresis, defecation ● Referred to as “rest and digest” system ○ Ex. person relaxing and reading after a meal ● Blood pressure, heart rate, and respiratory rates are low ● Gastrointestinal tract activity is high ● Pupils constricted, lenses accommodated for close vision Role of the Sympathetic division ● Mobilizes body during activity ● Referred to as “fight or flight” system ● Exercise, excitement, emergency, embarrassment activates sympathetic nervous ● Increased heart rate, dry mouth, cold sweaty skin, dilated pupils ● During vigorous physical activity ○ Shunts blood to skeletal muscles and heart ○ Dilates bronchioles ○ Causes liver to release glucose Key anatomical differences ● Three main differences between sympathetic and parasympathetic divisions ● Sites of origin ○ Parasympathetic fibers are craniosacral; originate in brain and sacral spinal cord ○ Sympathetic fibers are thoracolumbar; originate in thoracic and lumbar regions of spinal cord ● Relative lengths of fibers ○ Parasympathetic has long preganglionic fibers and short post ○ Sympathetic has short preganglionic and long post ● Location of ganglia ○ Parasympathetic ganglia are located in or near their visceral effector organ ○ Sympathetic ganglia lie close to spinal cord Parasympathetic Division ● Also called craniosacral division because fibers originate from brain stem and sacral regions or cord ● Long preganglionic fibers extend from CNS almost to target organs ● Synapse with postganglionic neurons in terminal ganglia that are close to or within target organs ● Short postganglionic fibers synapse with effectors Cranial Part of Parasympathetic Division ● Cell bodies are located in brain stem ● Preganglionic fibers run in ○ Oculomotor nerves (III): control smooth muscle of eye, cause pupils to constrict and lenses to bulge for focusing ○ Postganglion cell bodies located in ciliary ganglia within eye orbitals ● Facial nreves (VII): stimulate large glands in head

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Fibers that activate nasal and lacrimal glands have synapse in pterygopalatine ganglia ○ Fibers that activate submandibular and sublingual salivary glands synapse in submandibular ganglia ● Glossopharyngeal nerves (IX): stimulate parotid salivary glands ○ Fibers synapse in otic ganglia ● Vagus nerves (X): account for 90% of all preganglionic parasympathetic fibers in body ● Serve all thoracic and abdominal viscera ● Preganglionic fibers arise from medulla and synapse in terminal ganglia (intramural ganglia) in wall of target organs ● Cardiac plexus: slow heart rate ● Pulmonary plexus: serve lungs and bronchi ● Esophageal plexus: form anterior and posterior vagal trunks that sends branches to stomach, liver, gallbladder, pancreas, small intestine, and part of large intestine Sacral part of Parasympathetic Division ● Originates from neurons in S2-S4 and serves pelvic organs and distal half of large intestines ● Axons travel in ventral root of spinal nerves ● Branch off to form pelvic splanchnic nerves ● Synapse with ○ Ganglia in pelvic floor (inferior hypogastric plexus) ○ Intramural ganglia in walls of distal half of the large intestine. Urinary bladder, ureters, and reproductive organs Sympathetic Division ● Sympathetic is more complex and innervates more organs than parasympathetic ● Some structures are innervated only by sympathetic; sweat glands, arrector pili muscles of hair follicle, smooth muscles of all blood vessels ● Sympathetic also called thoracolumbar division ● Preganglionic neurons are in spinal cord segments T1-L2 ● Form lateral horns of spinal cord ● Preganglionic fibers pass through white rami communicantes and enter sympathetic ● There are 23 paravertebral ganglia in the sympathetic trunk ○ 3 cervical ○ 11 thoracic ○ 4 lumbar ○ 4 sacral ○ 1 coccygeal ● Upon entering sympathetic trunk ganglion, short preganglionic fiber may follow one of three pathways ● Synapse in trunk ganglia ○ Synapse with ganglionic neuron in same trunk ganglion ○ Ascend or descend sympathetic trunk to synapse in another trunk ganglion ● Synapse in collateral ganglia ○ Pass through trunk ganglion and emerge without synapsing in trunk (only in

abdomen and pelvis) ● Synapse outside of trunk in collateral ganglia Pathways from Sympathetic trunk ganglia to visceral effectors ● They can enter spinal nerves ● They can form cephalic periarterial nerves ● They can form sympathetic nerves ● They can form splanchnic nerves Spinal Nerves ● Axons of some postganglionic neurons leave the sympathetic trunk ○ Gray ramus ● Then merge with the anterior ramus of spinal nerves ● Gray rami communicates ○ “Gray”: unmyelinated axons ● Gray rami outnumber white rami ● Axons that leave the sympathetic trunk to enter the spinal nerves ○ Provide sympathetic innervation to skin of neck, trunk, and limbs ○ Including sweat glands, smooth muscle in blood vessels and arrector pili muscles of hair follicles Cephalic periarterial nerves ● Axons of the postganglionic neurons that leave the sympathetic trunk ● Extend to the head via wrapping and following arteries ● Provide innervation to visceral effectors in skin of face, head (lacrimal glands, pineal gland) Sympathetic nerves ● Axons of the postganglionic neurons that leave the trunk form the sympathetic nerves ● Extend to the visceral effectors in the thoracic cavity (heart and lungs) ○ Heart T1-T4 ○ Lungs (T2-T4) Splanchnic Nerves ● Those preganglionic nerves that pass through the sympathetic trunk without terminating in it ● Extend to the outlying prevertebral ganglia ● Abdominopelvic organs ○ T5-T9: greater Splanchnic nerve ○ T10-T11: lesser Splanchnic nerve ○ T12: least Splanchnic nerve ○ L1-L4: lumbar Splanchnic nerve ■ Terminate at inferior mesenteric ganglion ■ Supply distal colon and rectrum, urinary bladder, and genitals Adrenal Medulla ● Modified sympathetic ganglia ● Chromaffin cells ○ Similar to sympathetic postganglionic neurons except they lack dendrites and axons

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Release a mixture of catecholamine hormones ■ 80% epinephrine ■ 20% norepinephrine ■ Trace amount of dopamine ○ These hormones circulate throughout the body and intensify responses elicited by sympathetic postganglionic neurons Visceral reflexes ● Visceral reflex arcs have same components as somatic reflex arcs: receptors, sensory neuron, integration center, motor neurons, and effector ● Two key differences between visceral and somatic ○ Visceral reflex arc has two consecutive neurons in the motor pathway ○ Afferents fibers are visceral sensory neurons ■ Send info about chemical changes, stretch, or irritation ● Examples of visceral reflex: reflexes that empty bladder and rectum ● Visceral sensory fibers involved in phenomenon of referred pain ● Enteric Division: ○ Specialized collection of nerves and ganglia forming a complex, integrated neuronal network within the wall of the GI tract Neurotransmitters ● Two types: cholinergic( Ach) and adrenergic (NE) receptors ● Receptors are integral membrane proteins ○ Plasma membrane ○ Post synaptic neuron ○ Effector cell Cholinergic Receptors ● Two types bind ACh ● Named after drugs that bind to them and mimic ACh effects: Nicotine and Muscarine (Mushroom poison) ● Nicotinic ○ Found on: ■ All postganglionic neurons (sympathetic and parasympathetic) ■ Hormone-producing cells of adrenal medulla ■ Sarcolemma of skeletal muscle cells at neuromuscular junction ○ Effect of ACh at nicotinic receptors is always stimulatory ○ Opens ion channels, depolarizing postsynaptic cell ● Muscarinic ○ Found on: ■ All effector cells stimulated by postganglionic cholinergic fibers ○ Effect of ACh at muscarinic receptors ■ Can be either inhibitory or excitatory ■ Depends on receptor type of target organ ○ Ex. Binding of ACh to cardiac muscle cells slows heart rate, whereas bind to intestinal smooth muscle cells increases motility Adrenergic Receptors

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Two major classes that respond to NE or epinephrine Alpha ○ Divided into A1 and A2 ● Beta ○ Divided into B1, B2, and B3 ○ Effects depend on which subclass of receptor predominates on target organ ● Ex. NE binding to cardiac muscle B1, receptors causes increase in rate, whereas epinephrine causes bronchial relaxation when bound to B2 receptors Parasympathetic and Sympathetic Interactions ● Most visceral organs have dual innervation ● Action potentials continually fire down axons of both divisions, producing a dynamic antagonistic interaction ● Works to precisely control visceral activity ● Both ANS divisions are partially active, resulting in a basal sympathetic and parasympathetic tone ● One division usually predominates, but in a few cases divisions have a cooperative effect ● Agonist: a substance that binds to and activates a receptor Antagonistic Interactions ● Dynamic antagonism allows to precise control of visceral activity ● Sympathetic division increases heart and respiratory rates and inhibits digestion and elimination ● Parasympathetic division decreases heart and respiratory rates and allows for digestion and discarding of wastes ● Atropine: dilates the pupils Agonist Interactions ● Phenylephrine: found in cold and sinus medication to reduce production of mucus to relieve nasal congestion Autonomic tone ● Balance between sympathetic and parasympathetic ● Regulated by hypothalamus ○ Turn one up and one down ● 2 divisions can affect body organs differently ○ Postganglionic neurons release different neurotransmitters ○ Effector organs possess different adrenergic and cholinergic receptors Sympathetic tone ● Sweat glands, arrector pili hair muscles, kidneys, spleen, most blood vessels and adrenal medullae receive only sympathetic innervation ● Almost all blood vessel smooth muscle is entirely innervated by sympathetic fibers only, so this division controls blood pressure, even at rest ● During physical or emotional stress; sympathetic dominates ● Support vigorous physical activity And Rapid production of ATP and reduces body functions that favor storage of energy ● emotions like fear, embarrassment or rage stimulates the sympathetic division

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think of E situations ○ exercise, emergency, excitement, and embarrassment ● fight or flight ○ physiological response: pupils dilate, increase in heart rate and contraction, increase in blood pressure ○ liver releases glucose to increase blood glucose levels ○ Urine and digestion slow ● Longer-lasting and more widespread and parasympathetic stimulation affect ● sympathetic postganglionic axons diverge more extensively ● ACh: quickly and activates acetylcholine ● epinephrine and norepinephrine intensify and prolong the responses caused by norepinephrine Parasympathetic tone ● Enhances the rest and digest activities ● support body functions that conserve and restore body energy during times of rest and Recovery ● quiet intervals: parasympathetic dominate over sympathetic ● SLUDD: salvation, lacrimation, urination, digestion, defecation (increase) ● Decrease: heart rate, diameter of Airways, diameter of pupils (constriction) Cooperative effects ● Best example of cooperation between two divisions scene in control of external genitalia ● parasympathetic fibers cause vasodilation and are responsible for erection of penis or clitoris ● sympathetic fibers cause ejaculation of semen and males and reflex contraction of a female's vagina Clinical ● Autonomic neuropathy: damage to autonomic nerves that is a common complication of diabetes mellitus ● Early signs include sexual dysfunction ● other frequent symptoms include dizziness after standing suddenly ( poor blood pressure controls), urinary incontinence, sluggish eye pupil reactions, and impaired sweating ● Best way to prevent diabetic neuropathy is to maintain good blood glucose levels Control of ANS function ● ANS is under control of CNS centers in ○ brainstem and spinal cord, hypothalamus, and cerebral cortex ● hypothalamus is generally main integrative Center of ANS activity ● cerebral input may modify, ANS but does so subconsciously ○ Receives input relating to emotions from the limbic system to activate flight or fight ● Centers of hypothalamus controls ○ heart activity, blood pressure, temperature of body, water balance, and endocrine activity ● brainstem and spinal cord controls

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brainstem reticular formation appears to exert most direct influence over ANS medullary centers regulate heart rate and blood vessel diameter, as well as gastrointestinal activities ○ mid brain controls muscles of pupil and lens ○ spinal cord controls defecation and micturition but are subject to conscious override Disorders of the ANS ● Many a n s disorders involve deficient control of smooth muscle activity ● Hypertension ( high blood pressure) ○ over-active sympathetic vasoconstrictor response to stress ○ heart must work harder, and artery walls are subject to increased wear and tear ○ can be treated with adrenergic receptor blocking drugs ● Raynauds disease ○ Painful, exaggerated vasoconstriction in fingers and toes ○ digits turn pale, then cyanotic ○ treated with vasodilators ● autonomic dysreflexia ○ Life threatening, uncontrolled activation of autonomic neurons in quadriplegics and people with spinal cord injuries above T6 ○ blood pressure skyrockets, posing increased risk for stroke...